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enter image description here It's a smallish cut on the sidewall, and I don't think it goes deep enough to reach the cords. Thanks.

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    You've clearly never seen a tire blow up, or you wouldn't bother asking. I've had a (4-wheeled) wheelbarrow tire blow up while parked, it broke the ABS rim off and projected it over a 4m high wall after having bounced off a patio and a wall. Now imagine what if it wasn't stationary but driving in a busy city or motorway; and not a 10inch diameter wheel but a full car size. The only way this question makes sense if you don't have time to replace it before the MOT; but even then.
    – user3445853
    Jul 17, 2019 at 19:11
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    MOT implies the UK as a location - is that correct ? Different locations have different rules.
    – Criggie
    Jul 17, 2019 at 19:52
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    Hi guys, thanks very much for your answers. I will definitely get it replaced, its just I have the MOT tomorrow so did not have time to replace it beforehand
    – Paul Cameron
    Jul 18, 2019 at 11:22
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    Would love to hear the outcome of the MOT and also if the inspector explicitly identified the cut (or you asked) and if it was OK as-is.
    – Ian W
    Jul 19, 2019 at 22:40
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    Hi , the car failed it's mot on cv boots but the inspector didn't even mention the tire
    – Paul Cameron
    Jul 20, 2019 at 22:13

5 Answers 5

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If you can't see or feel the cords by lifting the edge of the cut with a blunt instrument (e.g. a coffee stirrer), then it shouldn't fail:

  • any ply or cord that can be seen without touching the tyre – fail

  • if by folding back rubber or opening a cut with a blunt instrument, so as not to cause further damage, exposed ply or cord can be seen irrespective of the size of the cut – fail

  • if a cut which is more than 25mm or 10% of the section width whichever is the greater, is opened with a blunt instrument and cords can be felt but not seen – fail

Source: UK MOT manual

However I'd still seriously think about replacing it, as it will have seriously weakened the sidewall, significantly increasing the risk of a blow-out.

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    I agree, don't think MOT, think safety.
    – GdD
    Jul 17, 2019 at 14:32
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    Where did the bullet items come from? Please provide source; sounds "official".
    – Ian W
    Jul 17, 2019 at 23:41
  • @IanW Sorry, my bad - I've added the link
    – Nick C ♦
    Jul 18, 2019 at 8:37
  • Thx. Same as in other post I referenced and can't bread as outside UK. Can you read further to see if it's applicable to the treads and / or sidewall? Totally different characteristics and tolerances.
    – Ian W
    Jul 18, 2019 at 8:43
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    @IanW The manual doesn't actually mention sidewalls at all, so I can only assume they intend the same rule to apply to both...
    – Nick C ♦
    Jul 18, 2019 at 11:46
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This question's answer How to assess the severity of a cut on a tyre sidewall probably best answers your question. I am blocked from accessing the link as outside the UK - relevant part of the testers' manual.

I think @Nick-C's advice applies to the tread, not the sidewall.

What I can tell you is that in (litigious) North America, most tire shops would refuse to even attempt to repair.

TireRack.com says:

Tires cut or punctured in the shoulder or sidewall areas, as well as any tires driven on while flat or with very low inflation pressure even for short periods of time are often damaged beyond repair and should be replaced. Driving on a tire while flat or with very low inflation pressure will permanently weaken the tire's internal structure, rendering it more susceptible to catastrophic failure.

Kaltire.com says:

But on the sidewall, those cords aren’t there. So, there’s just no way for a plug to fill that hole. The patch won’t hold, and it’s going to continue to leak.

In fact, I took in a tire that had a small ( < 0.5") screw still stuck in the side and they would not even touch it. Maybe they were trying to see me a new tire, but why would you risk a blowout?

Also, that's not a "smallish cut"; that's severe and has clearly compromised the integrity of the sidewall.

btw: every time you go over a bump in the road, the stress is transferred/absorbed via the sidewall first, which makes it more stressed than a patch on the tread.

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I personally would take it off, put the spare on, take the wheel and tyre to the service garage and get them to change it ASAP, I wouldn’t even drive to the garage with it on, if that goes whilst driving you are risking yourself and others.

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I'm an mot tester. The mot standard is the minimum requirement to be Road worthy just because you have an mot and it passes doesn't mean nothing will happen within 12 months till the next mot. That tyre will only fail if there are cords exposed or ply! Or if the vehicle examiner thinks that the cut is deep enough to reach the ply or cords, on the view of the picture I would advise would need the car and tyre in front of me to give a better judgment. My advise is to change the tyre anyway before the mot safety reasons thanks.

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I'm a tyre fitter and here in Northern Ireland that would be a fail as its a damaged side wall. And tbh if u value ur life I wouldn't be driving to fast on it.. If u want to risk it glue it back into place

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